Flextensional transducers are a type of transducer that may be used in underwater communications systems, i.e., sonar systems. Flextensional transducers may have wider bandwidths, lower operating frequencies, and higher power handling capabilities than other types of transducers of comparable size and weight.
Prior art flextensional transducers had a flexural outer shell which was usually elliptically shaped, and a piezoelectric ceramic stack of elements (used to excite the shell) which were placed between opposing interior walls across the major axis of the shell. When electrically actuated, the piezoelectric stack expands and contracts, thereby flexing the shell which, in turn, projects acoustic energy into a surrounding medium that is usually water.
Prior art flextensional transducers were relatively small (between 6 and 18 inches long, between 4 and 18 inches across the major axis and between 11/2 and 7 inches across the minor axis) and fully assembled, their maximum weight was approximately 80 pounds. Large flextensional transducers are used when it is required that the transducer have a higher power output and/or produce lower frequency signals. High acoustic power outputs and low resonant frequencies increase the range and hence, the utility of the transducer. A higher acoustic power output is generally achieved by designing transducers with a greater piezoelectric ceramic volume. This increased ceramic volume increases the weight of the transducer and some times the size of the transducer. Lower resonant frequencies are achieved by utilizing larger and/or thinner walled shells generally leading to larger and heavier transducers.
As flextensional transducers became larger and heavier, it became more and more difficult to support the transducer's piezoelectric stacks and shell, i.e., the active element, between the opposing interior walls of the flanges. One method provided by the prior art to support the active element involved the use of a neoprene boot or band which surrounded the shell/flange interface. The foregoing method required that the boot or band have sufficient strength to support the weight of the active element. As the transducer became larger and heavier, the boot or band no longer was able to support the active element. To relieve the boot of this excessive load, external tie rods were used. The aforementioned rods were fixed between the flanges to support the booted active element in any orientation. One of the disadvantages of the foregoing was that the interface between the tie rods and boots were subject to rapid erosion due to the acoustic activity at the interface. Another disadvantage of tie rod supports is that the tie rods would degrade the activity of the shell and the rods would be subject to bending moments. Thus, the size and weight of the transducer could not be continually increased by the foregoing method.